One of the key benefits of VoIP network services is to allow a subscriber to move between locations and still make and receive calls using the same phone number. The subscriber can be nomadic and the physical location of a VoIP endpoint can change, unlike an endpoint of the traditional Public Switched Telephone Network (PSTN) counterpart. For instance, a subscriber uses a customer premise based VoIP endpoint device, such as a Terminal Adaptor (TA) or a soft phone client, to access VoIP network services via a broadband access network at a home location. Later, when the subscriber travels to a different location, the subscriber can bring the same TA or soft phone client to access the same subscribed VoIP network services, e.g., using the same phone number making and receiving calls at the same calling rate regardless of location, via a different broadband network.
In order for an Enhanced 911 (E911) dispatcher at a Public Safety Answering Point (PSAP) to effectively provide emergency assistance to an E911 caller, the E911 dispatcher must have the phone number and the service address of the E911 caller. VoIP network providers are required to provide E911 services that are equivalent in reliability and performance to the PSTN counterpart. In a PSTN, E911 caller location is easily identified since the caller location is tied to a fixed service address associated with the calling phone number of a subscriber. However, in a VoIP network, E911 callers are nomadic due to the flexibility of advanced VoIP network services. This nomadic nature makes the identification of the actual service address of an E911 caller extremely difficult. If an E911 dispatcher does not have the correct service address of an E911 caller, an emergency dispatch can be sent to a wrong location. Failure to provide an accurate service address of an E911 caller due to outdated service address information can have serious or even fatal consequences. For example, a nomadic caller who is normally in New York and moves to California will be negatively impacted if an E911 call from the nomadic caller is forwarded to a PSAP in New York. Thus, it is important to properly route an E911 call to an appropriate PSAP.
Therefore, a need exists for a method and apparatus for detecting subscriber service address change in a packet network, e.g., a VoIP network.